Ohio and other states have lost an 'expert witness' in lethal injection death penalty cases.(Photo: Wikipedia)

A leading expert witness for states defending their lethal injection methods has ended his role, creating another potential hurdle for Ohio and other states scrambling to find workable execution systems.

Mark Dershwitz, a University of Massachusetts anesthesiologist and pharmacologist, was the witness called by Ohio in support of its new two-drug combination that led to a troubling 26-minute execution in January.

The same drug combination led to a nearly two-hour execution in Arizona last month.

Dershwitz has provided expert opinions for 22 states and the federal government over the past decade. He announced in June that he would no longer do so, saying he didn’t want to risk his professional license.

The news comes as states are running out of execution drugs and having difficulty finding alternatives.